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| Home > Publications database > Produktion und radiochemische Abtrennung von $^{147}$Gd zur Markierung und in vivo SPET-Evaluierung von Magnetopharmaka |
| Book/Report | FZJ-2019-01779 |
1997
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/21797
Report No.: Juel-3338
Abstract: There is a continuing interest in specific gadolinium compounds to be used in macroscopic amounts as MRI contrast agents in medical research. Their biodistributions are usually measured in animals using $^{153}$Gd (T$_{1/2}$ = 241.6 d) labelled analogues, which, however, cannot be used in humans. Fortunately, there is $^{147}$Gd, which may be able to bridge MRI and SPECT imaging techniques. The introduction of a new radionuclide for use in humans requires several development steps. With this aim nuclear data measurements were performed and a suitable target system for irradiations was developed. Furthermore a chemical separation procedure was worked out and SPET-phantom measurements, dosimetry and finally synthesis of two already known magnetopharmaceuticals with $^{147}$Gd were performed. Excitation functions were measured by the stacked-foil technique for the $^{147}$($^{3}$He,xn)-processes overthe energy range of 12 to 36 MeV, and the $^{144}$Sm($\alpha$,xn)-reactions over the energy range of 12 to 27 MeV. Thin samples of 96.5% enriched $^{147}$Sm$_{2}$O$_{3}$3 or 86.6% enriched $^{144}$Sm$_{2}$O$_{3}$ of 10 mm diameter and 2-5 mg/cm$^{2}$ thickness were prepared via a sedimentation method. Thick target yields of $^{147}$Gdwere calculated from the measured excitation functions and the levels of radiogadolinium impurities were determined experimentally. The optimum energy range at the compact cyclotron CV28 for the production of $^{147}$Gd via the $^{144}$($^{3}$He,3n)-process was found to be E3$_{He}$ = 36 $\rightarrow$ 13 MeV and via the $^{147}$Sm($\alpha$,n)-reaction as E$_{\alpha}$ = >27-13 MeV. The expected thick target yield of $^{147}$Gd over the respective energy ranges is 10 MBq/$\mu$Ah for the $^{3}$He-induced reaction and 4.8 MBq/$\mu$Ah for the $\alpha$-induced reaction. A target system was constructed which allowed irradiation of the target material Sm$_{2}$O$_{3}$ with 15 $\mu$A beams of 36 MeV $^{3}$He- or 27 MeV $\alpha$-particles. A separation technique involving cementation with Na-amalgam followed byan ion exchange process was developed to separate the n.c.a. gadolinium from the bulk of Sm$_{2}$O$_{3}$ target material and from the n.c.a. europium isotopes. The final purification of $^{147}$Gd was done using a small glass column (3 mm x 120 mm) or an HPLC column (8 mm x 300 mm) filledwith a cation exchanger. Using 97% enriched $^{147}$Sm and the separation technique described here about 60-70% $^{147}$Gd of high radionuclidic and chemical purity could be achieved. The chemical separation procedure developed also allowed an almost quantitative (>90%) recovery of the enriched target material for cyclic use. First SPET-phantom measurements were performed with the radiochemically isolated $^{147}$Gd. The measurement conditions of the TRIONIX 88 tomograph were optimized for this new SPET-nuclide. Especially the choice of suitable collimators, energy-window and reconstruction algorithms was important to compare $^{147}$Gd with commonly used SPET nuclides. Best results could be obtained with a middle- (MEUR) as weil as a high-energy (HEGP) collimator and the Butterworth reconstruction algorithm. Dosimetric calculations were done using available literature pharmacokinetic data of similar pharmaceuticals. The expected dose was compared with commonly used SPET radionuclides. Finally two commonly used magnetopharmaceuticals (Gd-DTAP, (Gd-DTPAkPolylysine) were synthesised and characterised. For $^{147}$Gd-DTPA an on-line process using a cation-exhange column was developed which gave a product of high radiochemical purity and yield (> 95%). For ($^{147}$Gd-DTPA)$_{n}$-Polylysine two classical routes, namely the mixed anhydrid and the bisanhydrid methods were performed. Both resulted in about 30% Gd-lysin-coupling (Gd carrier addded) via the DTPA-bridge. This was shown by NMR-measurements.
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